The present invention relates to a liquid crystal projector for projecting an image in liquid crystal panel, or the like image, enlarged on a screen; more specifically, a liquid crystal projector that can move the place of a picture projected on the screen by shifting the standing of projection lens up and down, and facilitates easy exchange of the projection lens. Cine film projection lenses can also be used in the present liquid crystal projector.
There have been projectors available in the market for magnifying and projecting an image in liquid crystal panel on a screen using a metal halide lamp, etc. as the light source. In such projectors, the light from a light source is concentrated via mirrors, or other such means, on a liquid crystal panel, and an image existing in the liquid crystal panel is projected through a projection lens on the screen.
Normally in a projector, the center of liquid crystal panel is located on the optical axis of projection lens, hence a picture is projected on a screen with its center and the optical axis of projection lens met. If standing of the projection lens is shifted upward relative to the liquid crystal panel, place of the picture on screen also shifts upward.
The projector is usually placed on a desk top. However, because a preferred positioning of projected picture is usually higher than the desk top, the projector is often uplifted in its front part by, for example, extending front feet of the projector. A drawback with the above described arrangement is that a projected picture is distorted to a trapezium shape. As means for solving the above described drawback, a projection apparatus is designed so, as it can shift the optical axis of projection lens relative to the center axis of liquid crystal panel, and project an image with the respective axes dislocated from each other.
It is a common practice with a floor setting type projector to shift a projected picture to be higher than the optical axis of projection lens; whereas with a ceiling-hanging projector, the projected picture is shifted downward.
Prior art mechanism""s for shifting the optical axis of lens are illustrated in FIG. 13-FIG. 14. FIG. 13 is a perspective view of such a mechanism disclosed in the Japanese Patent Laid-open No.5-27324. In which mechanism, a condenser lens 82 and a projection lens unit 83 mounted on an arm 84 may be moved up and down by turning a screw shaft 85. The optical axis is thus shifted from the center axis of a liquid crystal panel 81.
FIG. 14 is a side view of such a mechanism disclosed in the Japanese Utility Model Laid-open No.5-21246. In which mechanism, a projection lens 91 is placed on a pantograph pedestal supported with an operation link 92 and a link,93, and the projection lens 91 is shifted up and down, while being kept in parallel, by turning of a gear 94 engaged with the operation link 92.
A simplified version of the above mechanism is proposed by the inventor in the Japanese Patent Laid-open No.10-171044. The proposal is based on a basic concept of projecting a picture of 40 inch (approximately 1.0 meter) size on a screen placed at projection distance 1.5 m-2 m with a projection lens (hereinafter referred to as standard lens).
Generally, a projector is installed at an appropriate place considering the distance from screen. However, depending on given conditions of the projecting environment, a projector may be required to be located at a place closer to the screen, or at a place away from the screen. In such cases, the projection lens needs to be replaced with other lens that matches a given projection distance. In the mechanism as proposed in the Japanese Patent Publication No.H10-171044, how ever, cabinet has to be taken off and some of the inner structures need to be dismounted before it turns out to be possible to replace the standard lens with other projection lens. Thus the lens exchange requires a complicated operation, and is a time consuming operation.
The luminance level has become significantly higher with recent projectors. Speaking of the projection lens, a lens of long focal distance is needed to project a picture in a certain predetermined dimensions on a screen of a large hall, where there is a long projection distance to the screen from a projection apparatus installed in the back wall; whereas a projection lens of short focal distance is needed in a case of projection in a home theater, for example. It is requested for a projection apparatus to be compatible with varieties of lens systems of different focal lengths, in order to be able to comply with various projection environments, viz. various projection distances and various screen dimensions. The projection apparatus are also requested to have such a lens shift mechanism that can shift the standing of optical axis of a projection lens.
Any of the liquid crystal projectors having a lens shift mechanism, three-plate or single-plate configuration, have been designed so as to be able to shift the optical axis of projection lens relative to the center axis of liquid crystal panel. The lens shift mechanism employed in the above-proposed projection apparatus is complicated in the structure with a large number of assembly components; hence the projection apparatus are expensive in the manufacturing cost. Furthermore, it is difficult for the above mechanism to afford a sufficient quantity of shifting; the quantity of shift made available by the mechanism remains to be insufficient for meeting a targeted quantity of lens shift. (ref.: FIGS. 13, 14)
In most of the practical application environments, a place for installing a projector and a location where screen is located have been determined as fixed conditions that can not be changed (in a case of ceiling-hanging projector, for example, the distance to screen and the fixture on ceiling provided for installation of projection apparatus are already determined). After a projection apparatus has been installed on the fixture, the projection lens is shifted up or down to adjust the location of a projected picture. If a standard lens does not fit to the given projection distance, it needs to be replaced with other projection lens. The lens exchanging operation under such a circumstance is quite troublesome and time consuming.
In order to use a projection apparatus in a cinema hall, for example, where the screen dimensions and the distance thereto are already fixed, quite a number of various projection lenses have to be made available. It has been an earnest request among the customers in the projector market to use the conventional cine film projection lenses already at their hands in a liquid crystal projector.
The present invention addresses the above problems and tasks, and offers a liquid crystal projector that comprises:
a. a light source,
b. a group of mirrors for splitting/composing color beam from the light source,
c. a liquid crystal panel for controlling the transmission of color beam,
d. a lens holding member that can slide up and down provided with an opening,
e. a shift rod coupled revolvable with said lens holding member, and
f. a cabinet for housing said liquid crystal panel, said group of mirrors, said lens holding member and said shift rod, provided with a first hole at a place above said shift rod and a second hole at a place corresponding to the opening of said lens holding member.
A projection lens unit for enlarging and projecting an image of light transmitted from the liquid crystal panel can be mounted to the opening of said lens holding member, or detached therefrom, by turning the lens unit inserted through the second hole of the cabinet.
The lens holding member is formed of
a fixing section for fixing a projection lens at an end,
a fitting section for providing a sliding support, and
a nut section which is to be engaged with screw section of the shift rod.
The projection lens unit consists of a plurality of lens barrels and a plurality of unit lenses, and one of the lens barrels is provided with a fixing section for engagement with the lens holding member.
In a liquid crystal projector configured as above, the projection lens unit can be shifted up and down, furthermore the projection lens unit itself can be exchanged with other projection lens by a simple one-touch operation from the front face of cabinet.
The lens holding member is supported in a sliding manner by an optical base, on which optical base the liquid crystal panel is installed, with a sliding section that couples with the fitting section of the lens holding member. The lens holding member moves up and down while holding the projection lens unit as it is, along with revolution of the shift rod.
With a liquid crystal projector of the present invention, in which it has been configured so as a projection lens unit can be attached and detached through a second hole of the cabinet, both of the operations for exchanging projection lens unit and for shifting the projection lens unit up and down can be performed without taking the cabinet off the projection apparatus.
In a liquid crystal projector of the present invention, which has been configured so that the entire projection lens unit is integrated as a single-piece component detachable from the optical base, hardly any additional cost is required for implementing the above described mechanism, without incurring any increase in the number of assembly parts and components.
With a liquid crystal projector of the present invention, a standard projection lens may be exchanged to other projection lens at any time, without the need of taking the cabinet off the projection apparatus and dismounting constituent component parts and mechanisms down to a level at which the lens exchange operation turns out to be possible for the projection apparatus.
Thus, even in a situation where a place for installing projector and the screen location have already been determined and unchangeable, positioning of a projected picture can be adjusted by shifting the projection lens up or down, without causing a trapezium distortion. If a projection apparatus is tilted for adjusting the positioning of projected picture, the trapezium distortion is unavoidable with the projected picture. Furthermore, when a standard projection lens does not fit to the given projection distance, it can be replaced easily with other suitable projection lens.